Awesome! Good luck! I was too lazy, but something else I thought of was a big banner, google "suffragette" and you'll see some examples:
http://content.answers.com/main/content/wp/en-commons/thumb/d/da/300px-Suffragette_banner_carried_in_picket_of_the_White_House.jpg
http://www.geh.org/taschen/m197501122134.jpg
(What the banner says depends on the sort of steampunk you're going for, but you could have a lot of fun with it)

I'd be really interested to see pics of your costume when it's done, you should post it to feminist_fandom.